I don't interpret a soul mate only in a romantic sense. Sometimes when I read a book, let's say a philosophic one, I may feel that the author totally shares my perspective and I can relate to everything he/she says. It can be a character as well: that I'm exactly like that character from the story.
That said, unfortunately I don't think you will always be on good terms with your soul mate. Some say that opposites attract each other, some believe in 'similis simile gaudet'. Sometimes a soul mate is someone who understands you, sometimes he/she is very different, yet you feel a connection. In any case, it is someone who complements you. Bu it doesn't always comes naturally. Sometimes it takes a lot of time and effort.
In short, I don't think there is one destined soul mate, a perfect "other half of you" , but there are many people with whom you can connect and form bonds (key word is to form: I doubt that you can magically realize who is your soul mate without spending time together.)
I think everyone has their soul mate. There are billions out there, chances are high that there are people who share similar personality. But you have to search and find them. And even if you find them, it doesn't mean you can't lose them. Because people change- or, by getting to know them more and more, you realize they are not who you were looking for.
I have found very few people who shared a portion of my ideals and thoughts, let alone understanding me. On the other hand, I failed to understand some persons whom I really wanted to. In the end I couldn't keep them.